Make channelpadding_update_padding_for_channel() use !channel_is_client()

Because we need to include all relays, even if they are flapping in the consensus:

  // We should not allow malicious relays to disable or reduce padding for
  // us as clients. In fact, we should only accept this cell at all if we're
  // operating as a relay. Bridges should not accept it from relays, either
  // (only from their clients).
  if ((get_options()->BridgeRelay &&
       connection_or_digest_is_known_relay(chan->identity_digest)) ||
      !get_options()->ORPort_set) {

We should also use !server_mode() rather than !ORPort_set.